Renin

Renin, enzyme secreted by the kidney (and also, possibly, by the placenta) that is part of a physiological system that regulates blood pressure. In the blood, renin acts on a protein known as angiotensinogen, resulting in the release of angiotensin I. Angiotensin I is cleaved by angiotensin-converting enzyme, splitting off two amino acids from the 10-amino-acid chain of angiotensin I, to form angiotensin II. The resultant angiotensin II octapeptide (previously called hypertensin, or angiotonin) acts via receptors to constrict arterioles, causing a rise in both systolic and diastolic blood pressure. Angiotensin II is one of the most active vasoconstrictors known; on a weight basis it is significantly more potent than norepinephrine. It also increases the secretion of cortisol and aldosterone by a direct action on the adrenal cortex. Renin was discovered in 1898 by Robert Tigerstedt and Per Bergman, researchers at the Karolinska Institute in Stockholm. See alsorenin-angiotensin system.

in vertebrates and some invertebrates, organ that maintains water balance and expels metabolic wastes. Primitive and embryonic kidneys consist of two series of specialized tubules that empty into two collecting ducts, the Wolffian ducts (see Wolffian duct). The more advanced kidney (metanephros) of...